1. Field of Invention
This invention relates to marine seismic vibrators and more particularly to supporting structure for the vibrator which provide vibration isolation by attenuating the vibrations emanating at the inertial mass-vibrations that would be transmitted and damage supporting structure and towing structure during operation of the marine seismic vibrator.
2. Prior Art
Over the years many efforts have been made to provide a commercial marine seismic vibrator to utilize in marine operations the advantages offered by land based vibrators.
A typical marine vibrator is illustrated and described in U.S. Pat. No. 3,349,367 issued to S. S. Wisotski. Such vibrators comprise a sonic radiator driven by a hydraulic ram. The hydraulic pressures are derived from a surface source and applied by way of high pressure hoses to the hydraulic ram under control of a servo valve to effect movement of the sonic radiator over a predetermined frequency range. The vibrator is programed through control signals to generate energy in the seismic frequency band between 10 and 190 Hz. In conducting the operations the vibrator output is swept through a range of frequencies as above noted either in an upsweep or downsweep.
The inertial mass for the vibrator is provided by the structure housing the hydraulic ram and sonic radiator. Accordingly the housing such as that shown in FIG. 5 of the aforesaid patent will vibrate at the same frequency as the sonic radiator and these vibrations are transmitted to any structure mounted on the housing, for example, that utilized to connect the marine vibrator to surface supporting and towing means as well as to any equipment mounted to the structure near the vibrator.
The vibrational forces transmitted from the housing to the supporting structure attached thereto are significant. Water is a difficult medium in which to move structured parts. At the higher vibrational frequencies these forces moving the supporting structure in the water will cause the supporting structure literally to tear apart. Efforts at providing adequate supporting structure in view of these forces have in the past taken the form of massive metal components designed to have resonant frequencies outside the operating range of the vibrator. The result has been significant in increase in the weight of the marine vibrator assembly and with unsatisfactory results. These massive elements are torn apart at their juncture after but a few thousand sweeps of the marine transducer due principally to the forces encountered in moving such structure in water at the operating frequencies of the marine vibrator.
Accordingly it is an object of the present invention to provide supporting structure for the marine transducer which will withstand the forces encountered in moving objects at high speed in a body of water and significantly increase the life expectancy of such structures to give rise to a relatively light weight commercially viable marine seismic vibrator.